1. Field of the Invention
The invention relates to a device for detecting pericardial effusion following heart surgery.
2. Description of the Background Art
In almost every operation performed on the heart, heart valve replacement, bypass surgery, transplantation or fitting of a vascular prosthesis, the pericardium must be opened. Before doing so, it is necessary to cut through the skin, the subcutaneous fatty tissue and the sternum. The operation proper begins once the pericardium has been opened. First, the heart-lung machine is connected up in the same way in all operations. To do this, catheters with large lumina are introduced into the aorta, into the right atrium or the superior and inferior vena cava and into the right pulmonary vein, and the blood is circulated through these catheters once they have been connected up. The patient is cooled to a temperature of between 18xc2x0 C. and 32xc2x0 C. and the operation is then performed. In bypass surgery, the coronary vessels are dissected and connected to the bypasses; in heart valve replacement, the aorta and the right or left atrium are opened; in transplantation, all the major vessels leading to or from the heart are cut through and connected to the new heart. After the operation, the patient is warmed up again on the heart-lung machine and is then disconnected from the latter once the cardiovascular conditions have stabilized sufficiently. After inserting a number of drains to lead off the post-operative bleeding, the sternum is closed using wires and the skin is closed with sutures.
As will be evident from the described sequence of a heart operation, very large wound areas are created. If the patient has previously undergone heart surgery, cutting through existing areas of adhesion results in even larger wound areas.
In addition to these wound areas, from which hemorrhaging is possible, there is the further problem of anti-coagulation. To ensure that the blood does not coagulate in the heart-lung machine or in the tubes, medication is first used to render the patient""s blood incapable of coagulating. After the operation, medication is once again used to reverse this incoagulability, but this is not always entirely possible. The coagulability of the blood after heart surgery is also limited by the cooling of the body temperature and the contact with the foreign tissue of the heart-lung machine. Thus, after heart surgery, one is faced with the problem of very large wound areas and limited coagulability of the blood. This explains the post-operative bleeding which occurs in these interventions and which can amount to as much as 2000 ml in the first 24 hours after the operation. Replacing the lost blood with blood substitutes can further dilute the blood and thus dispose to hemorrhaging.
To channel off this blood, which gathers mainly in the pericardial sac, the aforementioned drains are inserted. If these drains become blocked, or if they come to lie in such a way that not all the blood can run off, this blood accumulates in the pericardium. If bleeding continues, this compresses the heart, because the pericardium cannot stretch. The result of this compression is that the heart can no longer fill properly and thus cannot pump sufficient blood through the body. This then results in a drop in blood pressure, an increase in central venous pressure, reduced elimination of urine and circulatory centralization. Radiography reveals a widening of the cardiac shadow. This situation is referred to as pericardial tamponade. It is a serious life-threatening situation for the patient; if follow-up surgery is not performed immediately to relieve the pericardium by removing the accumulated blood, this complication will have a fatal outcome.
Pericardial tamponade can only ever be diagnosed on the basis of its clinical picture. Radiography of the thoracic cage showing widening of the cardiac shadow is by itself not sufficient to permit diagnosis. An ultrasound examination is not always reliable since, after an operation, the tissue to be examined is often poorly visualized. In addition to this, both radiography and ultrasound examinations are only carried out when a concrete suspicion exists. This suspicion in most cases arises only when the abovementioned symptoms manifest themselves. However, prior to this suspicion arising, and during the required examinations, valuable time for the patient can be lost.
In the meantime the patient can deteriorate to such an extent that the operation has to be performed under emergency conditions. A delay in performing surgery or even emergency surgery of a pericardial tamponade can again have fatal consequences for the patient as a result of damage to other organ systems, such as the liver and kidneys, or possible infections, or it may considerably prolong the time the patient has to remain in intensive care.
The object of the invention therefore is to make available a device with which it is possible to continuously monitor the patient for a developing pericardial tamponade and to alert the physician or the nursing staff before the clinical symptoms occur.
This object is achieved by a device for detecting pericardial effusion, which includes a measurement apparatus connected to a wire probe to be anchored on the right heart ventricle and to at least one further wire probe to be anchored in a region of the pericardium, the measurement apparatus measuring and displaying the impedance between the wire probes and comparing the measured impedance values with a zero value or initial value and displaying the change in impedance.
Impedance measurements for recording tissue characteristics or oedemas are known in medicine. Thus, for example, U.S. Pat. No. 5,454,377 describes a method for recording the impedance in the myocardium. Current pulses are generated by means of two electrodes which are anchored in a part of the myocardium, which current pulses generate a voltage between the electrodes. [lacuna] By an impedance spectrum which is characteristic of the myocardial state.